MySQL 查询设置 NULL 值
mysqlmysqli database更新于 2025/10/30 17:16:17
使用 IS NULL 查找 NULL 值并使用 MySQL UPDATE 和 SET 更新新值−
update yourTableName set yourColumnName=yourValue where yourColumnName IS NULL;
首先我们创建一个表 −
mysql> create table DemoTable768 ( Clientid int NOT NULL AUTO_INCREMENT PRIMARY KEY, ClientName varchar(100), ClientAge int ); Query OK, 0 rows affected (0.47 sec)
使用 insert 命令在表中插入一些记录 −
mysql> insert into DemoTable768(ClientName,ClientAge) values('John',23);
Query OK, 1 row affected (0.21 sec)
mysql> insert into DemoTable768(ClientName,ClientAge) values(NULL,26);
Query OK, 1 row affected (0.11 sec)
mysql> insert into DemoTable768(ClientName,ClientAge) values('Carol',28);
Query OK, 1 row affected (0.53 sec)
mysql> insert into DemoTable768(ClientName,ClientAge) values(NULL,24);
Query OK, 1 row affected (0.16 sec)
使用 select 语句显示表中的所有记录 −
mysql> select *from DemoTable768;
这将产生以下输出 -
+----------+------------+-----------+ | Clientid | ClientName | ClientAge | +----------+------------+-----------+ | 1 | John | 23 | | 2 | NULL | 26 | | 3 | Carol | 28 | | 4 | NULL | 24 | +----------+------------+-----------+ 4 rows in set (0.00 sec)
以下是设置 NULL 出现值的查询 −
mysql> update DemoTable768 set ClientName='Chris' where ClientName IS NULL; Query OK, 2 rows affected (0.41 sec) Rows matched: 2 Changed: 2 Warnings: 00
让我们检查一下视图的描述 −
mysql> select *from DemoTable768;
这将产生以下输出 -
+----------+------------+-----------+ | Clientid | ClientName | ClientAge | +----------+------------+-----------+ | 1 | John | 23 | | 2 | Chris | 26 | | 3 | Carol | 28 | | 4 | Chris | 24 | +----------+------------+-----------+ 4 rows in set (0.00 sec)
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